Systems have heretofore been devised for exposing a given field of view to either a mosaic array of detectors, or a scanning linear array of detectors to develop information regarding the characteristics of such field of view. That is, infrared detectors have heretofore been utilized to develop electrical signals as to certain characteristics of such fields in order to develop a record thereof.
A further extension of that basic idea has been to repeat such scanning or gathering of information of a given field of view so as to be able to compare the signal levels from the different frames to thereby enable differences to be detected. Such differences represent an indication of a change in infrared values from one frame to another. This generally indicates motion within such field of view such that something or someone has entered the field, or has moved from one position to another within such field of view.
Within the recent past, such process has been automated so that such process which is called frame-to-frame differencing can take place within an extremely short period of time. Also, the signal levels of the differences between such frames can be utilized in conjunction with a cathode ray tube to provide a visual display of whatever motion may have occurred within the particular field of view.
As will be realized by those persons skilled in the art, such frame-to-frame differencing requires that the several frames to be compared by being subtracted from each other must correspond very precisely to insure that there is no change in the relationship between the detector array and the field of view for the several frames. That is, any physical motion due to the lack of a firm, stationary mounting means or platform for the detector array and its actuating means, if such there be, will produce a difference signal between the compared frames which, of course, is not related to the motion of a target within the field of view. Such erroneous difference signals render the results meaningless or at least less than optimal for the intended purposes.